Display device having an extendible screen

ABSTRACT

A display device ( 1 ) has an extendible screen ( 2 ) and at least one extendible side member ( 3 ). The extendible screen ( 2 ) is extendible in an extension direction from a relatively compact form to an extended form. The screen ( 2 ) in the extended form has opposed edges ( 17 ) that are substantially parallel to the extension direction. An extendible side member ( 3 ) is provided for at least one of said opposed edges ( 17 ). The or each extendible side member ( 3 ) is extendible to provide support to and structural rigidity to the screen ( 2 ) when the screen ( 2 ) is in the extended form. The display device ( 1 ) provides an extendible rigid screen ( 2 ) suitable for example for creating a rigid collapsible tablet computer, or enabling a compact portable display to support a rigid touch-screen, or for incorporation into a mobile phone or remote control unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 10/873,561 filed Jun. 22, 2004, which claimspriority to U.S. Provisional No. 60/480,843 filed Jun. 23, 2003, thedisclosures of which are incorporated herein by reference.

The present invention relates to a display device having an extendiblescreen.

There is growing demand for extendible screens for displaying textand/or graphics for use with computers or other electronic and mobiledevices. As computing power relative to size increases, it is possibleto make electronic devices in ever smaller sizes to meet consumerdemand. However, one of the limiting factors encountered with thisminiaturization of technology is in the user interface. Specificallyreferring to the screen, as the screen is reduced in size the amount ofinformation it can relay is also reduced until a point where it isimpractical for the user to use.

In several prior art documents, for example U.S. Pat. No. 6,311,076,US-A-2001/0003450, JP-A-2000/132122 and JP-A-1999/272205, theconflicting demands of providing a small screen for portability and alarge screen for useful display of information are addressed byproviding flexible screens which can be arranged in more than one form.In each case, a flexible screen can be rolled into a compact form whennot being used and unrolled into an extended form for the display ofinformation. The screen is rolled about either one or two axes when inthe compact form. The prior art arrangements however have a number ofshortcomings, which the present invention addresses.

According to the present invention, there is provided a display device,the display device comprising: an extendible screen that is extendiblein an extension direction from a relatively compact form to an extendedform, the screen in the extended form having opposed edges that aresubstantially parallel to the extension direction; and, an extendibleside member for at least one of said opposed edges, the or eachextendible side member being extendible to provide support to andstructural rigidity to the screen when the screen is in the extendedform.

The present invention provides an extendible screen with at least oneextendible side member in order to provide at least some structuralrigidity to the screen when in the extended form. The display device iscapable of being arranged in a compact form, for example for storage ortransportation purposes. However it is also capable of being deployedwith the screen in at least one extended form, with the or each sidemember also extending to provide support to the screen. The structuralrigidity given to the extended screen allows it to be used in a widerrange of applications than would otherwise be possible. For example, thescreen is capable of being placed on an irregular surface whilst stillretaining its flatness. This is in contrast to prior art devices withflexible screens but no support which would need to be held in positionby external means or placed on a flat surface of sufficient size. Inaddition, the support given to the screen can allow the device to beheld in one hand, leaving the other hand to provide input to the devicefor example. The screen is also more suitable to incorporate atouch-sensitive input device. The support and rigidity given to thescreen by the or each side member allows the flexible screen to receivetouch input without deforming under the pressure of the input. Inaddition the side member provides a solid edge which protects thepotentially delicate edge of the screen. The side member also gives thedisplay device a more solid, robust look and feel. Overall this providesthe advantage of a solid tablet display with significantly increasedportability and flexibility in terms of screen size and application.

In a preferred embodiment, the display device comprises a respectiveextendible side member for each of said opposed edges. This givesgreater structural rigidity to the display device and more completeprotection from damage to the potentially delicate edges of the screen.In one preferred arrangement, the screen can be tautly suspended betweenthe two side members providing further support to the screen.

In a most preferred embodiment, the or at least one of the side membersis provided by a bistable material having a first stable state when saidside member is extended and a second stable state when said side memberis not extended. Bistable materials per se are known and are capable offorming two stable structural forms (see U.S. Pat. Nos. 6,256,938 and6,217,975 for example). In other words a bistable material can transformbetween a first stable form and a second stable form and are typicallycapable of bearing significant physical loads when in their stableforms. Hence they can be employed in the present invention to provideside members that have a first stable form in which the side members arein a compact form and a second stable form in which the side members arein an extended form, and are capable of bearing load. Furthermore, thepreferred bistable material can exist with one end in one stable formand the other end in a second stable form, the bistable materialtherefore being capable of forming extendible side members that can beextended to any desired length.

In an embodiment, the screen is extendible to and lockable at anintermediate position between said relatively compact form and saidextended form, the or each side member being extendible to providesupport to and structural rigidity to the screen when the screen is inthe intermediate position. The screen can thus be extended to thedesired size according to the application and locked into position. Ascreen of the desired size can thus be formed, such sizes including forexample a large “tablet” computer mode, a “widescreen” for play back ofmovies, an A4 size screen for displaying documents or web pages, and asmaller A5 size screen for use with a PDA device. The side members alsoprovide a uniform appearance of the device at each size.

In a preferred embodiment, the display device comprises a bar extendingbetween said opposed edges, the bar being fixed to the screen and the oreach side member. Such a bar can be used to aid in the extension and/orretraction of the screen. The bar can be fixed to the screen and the oreach side member to set their relative position and to ensure that theircorrect alignment is maintained. In addition, the bar can be used tomark the midpoint, or any other convenient point, of the screen toprovide a reference point, and used to fix the or each side member inits load-bearing form at its midpoint. This can be achieved in a simpleway in a preferred embodiment by providing the bar with an end profileshaped to lock the side member in its load bearing form. Also, in theembodiment where the screen is rolled about two axes, the bar can beused to define a boundary defining which part of the screen is rolledabout which axis. The bar can also be used as part of a mechanism toimplement this.

The display device may comprise a locking mechanism for locking the orat least one of the side members in its extended form.

In a preferred embodiment, the display device comprises at least onehousing which at least partially accommodates the screen when in saidrelatively compact form, wherein the or at least one of the side membersis at least partially accommodated by the housing when the screen is insaid relatively compact form. The housing preferably has a guideaperture through which said side member passes on extension orretraction of the screen in order to guide the movement of said sidemember between the extended and retracted states of said side member.This is particularly useful in the case of the side member being formedfrom a bistable material because the guide apertures can be shaped toaid the transition between the two stable states of the side member asit passes through the aperture.

In another preferred embodiment, at least one of said opposed edges ofthe screen has a groove which receives a tongue of the correspondingside member when the screen is in the extended form. In a furtherpreferred embodiment, the tongue is provided by an edge of the sidemember. This tongue and groove arrangement between the side member andthe screen edge helps to lock the screen to the side member and maintainthe side member in an open stable state, and can be arranged to allowforce to be transmitted between the side member and the screen. Hencewhen both sides of the screen are locked to side members in this way,the flexible screen can be tautly suspended between the two rigid sidemembers, thus providing further rigidity to the screen. This locking canexist along the length of the extended screen edges, thus allowing aneven distribution of force across side members. Such an arrangement canbe dynamically formed, meaning that, in an embodiment where a guideaperture is provided, each part of the tongue and groove engage witheach other as and when they are extended through the guide aperture.Accordingly when the screen and side member(s) are not extended, theycan be stored separately from each other. This allows the two to bestored in different fashions, allowing flexibility in the storagearrangements (and manufacture) of the screen and side member(s) andtherefore permitting the compact form of the device to be small.

In a most preferred embodiment at least one of said opposed edges of thescreen has plural projections which are received by respective pluralapertures or recesses on the corresponding side member when the screenis in extended form to provide a reversible locking arrangement betweensaid screen edge and said side member. The apertures/recesses andprojections provide a further or alternative locking arrangement betweenthe extended portions of the screen edge and the corresponding sidemember to that of the tongue and groove arrangement of the previouslydescribed embodiment. The locking arrangement of the apertures/recessesand projections may provide the same advantages as the tongue and groovearrangement. In addition the locking arrangement of theapertures/recesses and projections restricts relative movement betweenthe side member and corresponding screen edge in a longitudinaldirection.

In a most preferred embodiment, the display device comprises at leastone guide member for at least one side member, the or each guide memberbeing arranged to guide the side member and screen edge into or out oflocking engagement on extension or retraction respectively of said sidemember and screen. In this instance, upon retraction of the screen andside member, the guide member guides the side member so that theapertures/recesses of the side member disengage from the projections ofthe screen edge. After disengagement, the guide member may provide thefurther advantage of guiding the side member and screen edge such thateach is guided into a respective storage region inside the housing.

In a most preferred embodiment, the side member has a firstcross-sectional shape when in its extended form and a secondcross-sectional shape when in its retracted form, the housing has aguide aperture through which said side member passes on extension orretraction of the screen, and said side member has a tongue provided byan edge of said side member and the corresponding edge of said screenhas a corresponding groove, wherein said guide aperture is arranged toguide the transition of said side member between its first and secondshapes on retraction and extension of the side member respectively andto cause said tongue to engage with said groove on extension of the sidemember. The guide aperture of this embodiment has the dual function ofaiding the transition of the side member between its retracted form andits extended form as the screen is extended and retracted, and aidingthe formation of the tongue and groove engagement between the sidemember and the screen as the side member and screen are extended.

In an embodiment, the screen comprises a screen backing layer formedfrom a plurality of substantially parallel slats arrangedperpendicularly to the extension direction.

In an embodiment, the screen comprises a screen backing layer formedfrom a bistable material that has increased rigidity when planar. Inanother embodiment, the screen comprises a screen backing layer formedfrom a smart material that has increased rigidity when planar and iscapable of undergoing a current-assisted solid-state phase transition.These arrangements of the screen backing layer provide the screen withincreased rigidity when the screen is in its extended form, anddecreased rigidity, which provides the advantage of aiding the screen toassume and maintain a compact form.

In a further preferred embodiment, the screen is arranged to roll fromthe extended form to the relatively compact form. In one embodiment, therolling screen rolls about a single axis. However, in a preferredembodiment, the rolling screen rolls partly about a first axis andpartly about a second parallel axis.

The display device in a preferred embodiment is capable of providing anextendible rigid screen suitable for creating a rigid collapsible tabletcomputer, or enabling a compact portable display to support a rigidtouch-screen, or for incorporation into a mobile phone or remote controlunit.

Embodiments of the present invention will now be described by way ofexample with reference to the accompanying drawings, in which:

FIG. 1 shows a perspective view of a first example of a display deviceconstructed in accordance with an embodiment of the invention;

FIG. 2 shows a perspective view of the display device of FIG. 1 incompact form;

FIG. 3 shows a perspective view of the display device of FIG. 1 in anextended form with the screen removed for clarity;

FIG. 4 shows an enlarged detail of FIG. 3 shown from above;

FIG. 5 shows a partially sectioned enlarged detail of FIG. 3 shown inperspective;

FIG. 6 shows a cross-section of one of the side members of the firstexample interlocking with a side of the screen;

FIG. 7 shows a partial cross-section of the display device of FIG. 1taken through the cross-bar;

FIG. 8 shows a perspective view of a second example of a display deviceconstructed in accordance with an embodiment of the invention;

FIGS. 9 a, 9 b and 9 c show a perspective view of the display device ofFIG. 8 in compact form;

FIG. 10 shows a perspective view of the display device of FIG. 8 in anextended form with the screen removed for clarity;

FIG. 11 shows an enlarged detail of FIG. 10 shown from above;

FIG. 12 shows a partially sectioned enlarged detail of FIG. 8 shown inperspective;

FIG. 13 shows a cross-section of one of the side members of FIG. 8interlocking with a side of the screen; and,

FIG. 14 shows a partial cross-section of the display device of FIG. 8taken through the cross-bar.

Referring to the drawings, a display device 1 comprises a rollablescreen 2 with two opposed side members 3. The rollable screen 2 isrolled at each ends about one of two opposed parallel rollers 4. Eachroller 4 is mounted in a housing 5 and is free to rotate about its axis.An aperture 6 in the face of the housing 5 allows the screen 2 to passinto and out of the housings 5. The arrangement of the housings 5 androllers 4 at each end of the screen 2 is identical in construction andoperation and so only one wilt be described in detail in the following.This symmetric construction is an advantage of the preferred embodimentas it helps to keep down manufacturing costs.

Referring to FIG. 4, a detailed view of part of the housing 5 is shown.At each end of the roller 4 there is a pin 7 which is co-aligned withthe axis of the roller 4. Each pin 7 is received by a complementaryrecess 8 formed in the housing 5 which holds the roller 4 in positionwhilst allowing it to rotate about its longitudinal axis. A pair of rollbar guides 9 are positioned adjacent to the housing aperture 6, beingpositioned parallel to the roller 4, with one roll bar guide 9 above theother to form a roll bar aperture between them which is narrower thanthe housing aperture 6. This roll bar aperture acts as a guide for thescreen 2 as it moves back and forth through the housing aperture 6. Theroll bar guides 9 are retained at their ends by brackets 11 formed inthe interior of the housing 5. The brackets 11 hold the roll bar guides9 in position whilst allowing them to rotate about their axes. Hence, aswell as guiding the screen 2, the smooth and rotatable nature of theroll bar guides 9 reduce frictional wear and other stresses on thescreen 2 as it passes through the housing 5.

Referring to FIG. 3, a similar view to FIG. 1 but with the screenremoved for reason of clarity, an X-frame 12 is shown attached to thetwo opposed housings 5. The X-frame 12 is positioned immediately underthe screen 2. In the embodiment shown the X frame 12 is comprised of twotelescopically extendible members 13, 14, which are pivoted together attheir midpoints. Each end 15 of each X-frame member 13, 14 passes intothe housing 5 through the housing aperture 6 and is attached to aninterior surface of the respective housing 5 in such a way that allowsit to pivot. The X-frame 12 provides further structural rigidity to thedisplay device 1. The X-frame 12 can also be used to limit the maximumextension of the screen 2.

One continuous, extendible side member 3 is disposed at each side of thescreen 2. Each end of each side member 3 is accommodated by a respectivehousing 5 which it enters through a guide aperture 24. As the screen 2extends or retracts from the housing 5, the side members 3 also extendor retract from the housing 5 to provide a continuous, structurallyrigid edge to the screen 2. This arrangement provides severaladvantages.

First, it provides added structural rigidity to the device 1 as a wholeand to the screen 2 in particular. This gives several beneficialcapabilities to the device 1 when being used in its deployed mode. Forexample, the device 1 can be held in one hand, or in both hands, orplaced on an uneven surface, whilst maintaining its form. Secondly, itprovides support and stiffness to the screen 2, allowing it to maintainits flatness. As well as providing the advantages of a flat displaysurface, this can also prevent damage to the screen 2 where it is madeof a technology susceptible to damage from sharp bending of its surface.Thirdly, the solid edge provides protection for the edge of the screen 2from damage from external sources, as well as giving the device 1 asolid, rigid look, which is substantially uniform regardless of theextended length of the screen 2.

Similarly, an extendible backing layer 32 can also be provided. This canbe positioned beneath the screen 2, extending between the side members3, and in combination with the side members 3 would encase the parts ofthe screen 2 other than the display surface itself. This would allowcircuitry or other components positioned under the screen to be hiddenfrom view and protected from damage. This would also provide a moreaesthetically pleasing, solid appearance to the device 1, which makesthe device 1 more appealing to consumers, and can increase further therigidity of the screen 2.

The backing layer 32 may be in the form of plural parallel slats whicheach extend across the width of the screen 2 and have increased rigidityby locking into the side member using, for example, a tongue and groovearrangement. (Such slats 35 are shown in the second example discussedbelow.)

Alternatively or additionally, the backing layer 32 can be formed, inwhole or in part, from a bistable or smart material (such as a shapememory alloy) that has some increased rigidity in the flat deployedconfiguration. Such a smart material can utilise a pseudo-elastic effect(which can be enhanced, for example, by passing a current through thelayer) to increase flexibility or undergo a solid-state phase change asthe screen 2 rolls about the rollers 4.

A cross-bar 16 is attached to the underside of the screen and runsacross its width parallel to the rollers 4. The two ends of the bar 16are attached to the two side members 3 respectively. As shown moreclearly in FIG. 7, an end profile 31, which in the preferred embodimenthas a shape corresponding to the cross-sectional shape of the sidemember 3 in its open extended form, is formed at each end of thecross-bar 16 to lock the side members 3 in their load bearing form. Inthe preferred embodiment the cross-bar 16 is positioned at the midpointof the screen 2 and the midpoint of the two side members 3. Thecross-bar 16 serves a number of purposes. First, it acts as anadditional support for the screen 2. Secondly, it provides a permanentconnection between the screen 2 and the side members 3 at theirmidpoints which has the effect of maintaining their correct relativealignment and holds the midpoints of the side members 3 in theirload-bearing bistable form at all extensions between fully compact andfully extended. Thirdly, it acts as a reference marking the midpoint ofthe screen 2 which can be used when retracting the screen or extendingit to the desired position. Optionally the cross-bar 16 and the X-frame12 can be attached to each other at their midpoints to further aid thisprocess.

In the preferred embodiment the side members 3 are formed from abistable material, such as are known per se. Bistable materials have theproperty of being able to take on two stable structural forms. Hence amember made using a bistable material is capable of forming two stablestructures. Furthermore such a member can have one of its ends in afirst stable state, and the other end in a second stable state, withoutsignificant instability. Bistable materials are also capable of formingmembers capable of bearing considerable loads. They are therefore wellsuited to the side members 3, as in a first stable state they can forman extended member capable of bearing load and providing support to thescreen, and in a second stable state they can take on a more compactform which is stable.

Referring now to FIGS. 5 and 6, a cross section of a bistable sidemember 3 and part of the rest of the device 1 is shown. In its extendedform, each side member 3 has a cross-sectioned shape that isapproximately an inverted tear-drop, though with one edge 22 slightlymore inboard that the other edge 23.

In the preferred embodiment the side members 3 lock to the edges of thescreen 2 as the screen 2 is extended. A screen edge strip 17 is attachedto each side of the screen 2 and runs along the extent of its length.Each screen edge strip 17 has an upper groove 18 and a lower groove 19running along its length. When the screen 2 is extended, the edges 22,23 of the side members 3 locate into the lower groove 18 and uppergroove 19 respectively of the respective screen edge strips 17. Thecombination of the screen edge strip 17 with the bistable side members 3“locked” into it provides a structurally rigid tubular member capable ofbearing considerable load. This provides structural rigidity to thedisplay device 1 as a whole, as well as supporting the screen 2 andconstraining its edges, providing resistance to deformation of thescreen.

In the compact form, each side member 3 is almost entirely in arelatively flat form. When in this form, the two legs of the lowerV-shaped section 26 close together, whilst the upper curved section 27flattens out so the section as a whole is substantially planar.Referring to FIG. 4, the end of the side member 3 which is accommodatedwithin the housing 5 takes on this relatively flat form and isaccommodated by channels 28 in the rear wall of the housing 5.

In order to aid the transition of each side member 3 between its twostable forms as it passes between the interior and exterior of thehousing 5, the channel 28 stops short of the guide aperture 24 and theguide aperture 24 is shaped according to the two forms of the bistablematerial. Preferably, the guide aperture 24 has a shape intermediate thecross-sectioned shape of the side member 3 at its two stable forms. Inother words, the guide aperture 24 is shaped to correspond to the shapeof the side member 3 at its transition between the two stable forms. Ina further embodiment, sprung bearings and/or roll-bars (not shown) canbe positioned adjacent to the channel 28 and guide aperture 24 andarranged to aid the transition. (An example of this arrangement is shownin the second example discussed below.)

Accordingly, as each side member 3 is extended out of the housing 5, itpasses through a transition 29 at which the two legs of the lowerV-section 26 spring apart and its edge 23 is guided into position tolock into groove 19 of the screen edge strip 17, whilst the upper curvedsection 27 curls over to allow its edge 22 to lock into the upper groove18 of the screen edge strip 17. This provides a “zip-fastening” effectbetween each side member 3 and screen edge strip 17, the side members 3and edge strip 17 “locking” together as the side members 3 extendthrough their respective guide apertures 24.

In an additional embodiment, in place of a bistable material, the sidemembers 3 can be formed from a material having a single intrinsic stableform, with a second stable form being achieved by the use of a magneticstrip. For example, the V-section 26 of side member 3 can have a firststable form where its two legs spring apart, and a second stable formwhere its two legs are held together by the action of a magnet on one ofthe legs and exerting a magnetic attraction to a magnetic element on theother leg. The guide apertures 24 again aid the transition between thetwo stable forms.

It will be appreciated that the display device 1 is in principal capableof being deployed in any intermediate configuration between the fullyretracted, compact form and its fully extended form if desired.

Referring to FIG. 2, the display device 1 is shown in its most compactform. The screen 2 is fully retracted and the housings 5 have cometogether to abut each other. The housings 5 can be locked together inthis state with a latch (not shown) to prevent the device 1 fromextending unintentionally. The screen 2 is rolled about the two rollers4, the cross-bar 16 is accommodated equally in two recesses in thehousings 5, the X-frame 12 has telescopically retracted, and the sidemembers 3 have largely retracted into the housing 5, having assumedtheir relatively flat form, and are accommodated in the channels 28.

There are various options for deploying the device 1. For example, thehousings 5 could be manually separated until the screen 2 achieved thedesired width. Alternatively or additionally, one or both rollers 4could be motor driven to allow the device to automatically produce ascreen 2 of the desired width/length. The rollers 4 could be springloaded to bias the device 1 to a pre-selected configuration. A brake(not shown), such as a friction pad bearing on one or both side member 3can be incorporated into one or both of the housings 5 to allow thescreen 2 to be locked into position in either a closed or partially orfully deployed configuration. This brake may be manually or electricallyoperated for example.

It is possible for the display device 1 to be deployed in more than oneconfiguration, allowing screens 2 of different sizes and aspect ratiosto be formed appropriate to the application for which the device 1 isbeing used. It is possible to completely automate the deployment of thescreen 2. Controls 30 on the housing 5 may be used by the user to selectan application that the device is to be utilised for (for example PDA ortablet mode). The device 1 could then automatically extend the screen 2to the appropriate size and then lock it in place. The degree of screenextension could be determined for example by measuring the amount ofrotation of the rollers 4 using electronic or optical means, suchmeasuring techniques being known per se.

The screen 2 itself can be made from an organic LED (OLED) or polymerliquid crystal technology. The screen 2 can be combined with othertechnologies such as a flexible circuit control membrane to drive thedisplay, and/or a flexible ion-polymer battery for power supply, and/orelectro-luminescent cable to back-light the display. Alternativelycircuitry, batteries or other components can be stored inside therollers 4, or elsewhere in the housing 5.

In addition, the screen 2 can be used for input as well as display. Atouch-sensitive screen 2 can be implemented by adding charge gridtechnology to the screen 2. Sufficient support is given to the screen 2to provide a substantively solid surface, permitting touch-sensitiveoperation. The X-frame 12, cross-bar 16 and particularly the sidemembers 3 all provide support to the screen 2, whilst the “zipfastening” interface between the side members 3 and the screen edgestrips 17 constrain the screen edges to provide a stiffening effect,further adding to its ability to resist deformation of its surface. Inaddition, ribs or slats (not shown) can be embedded in the screenbacking 32 running parallel to the rollers 4. These would provide addedstiffness to the screen 2 in this direction, whilst not affecting thescreen's ability to roll about the rollers 4. Such ribs may have a crosssectional shape that is square or rectangular or some other shape, suchas a sector of a circle.

The display device 1 can also be used with a simpler screen 2, such as astatic solid state screen combined with a magnetic print head/refreshbar in the housing 5 which resets the image each time the device 1 isopened. This would allow applications such as digital newspapers, keydocuments or web site display.

The display device 1 can be combined with other technology to provideother applications. CPU and other processing means could be encased bythe housing 5. Communication devices can be encased in the housing 5 toallow the device 1 to access and display web pages, for example. USBconnectivity can be added to allow interfacing to other externaldevices. Input devices can be associated with the housing 5. Forexample, pointing devices such as a tracker ball or mouse “nubbin”and/or hot keys can be provided in one of the housings 5 at anergonomically suitable position.

Referring now to FIGS. 8 to 14, a second example of an embodiment of thepresent invention is shown. Like reference numerals are used forcorresponding features in the first example (shown in FIGS. 1 to 7) andthe second example. The second example differs from the first exampleonly in certain features and accordingly not all features of the secondexample will be discussed in detail here. Generally speaking the secondexample differs from the first embodiment in that the housings 5 aremore stylised, the channels 28 are positioned in front of the rollers 4rather than in the rear wall of the housings 5, and there is a differentlocking arrangement concerning the side members 3 and the screen edgestrips 17, which allow among other things a reduced cross-sectionprofile of the side members 3.

FIG. 8 shows the display device 1 in a deployed configuration with thelid 33 of each housing 5 removed for clarity. The housings 5 support therollers 4 which are attached to the screen 2 and side members 3 whichare attached to the screen edge strips 17. The screen edge strips 17 inthis example form the top face of the side structure rather than theinterior.

FIG. 9 a shows the display device 1 in its collapsed configuration. FIG.9 b shows the profile of the screen 2 when fully stored and rolledaround the rollers 4. FIG. 9 c shows the device with the lids 33attached to the housings. The lids 33 preferably provide a viewingwindow 34 to allow the screen to be partially visible in the collapsedconfiguration.

FIG. 10 shows the display device 1 with the screen 2 and housing lids 33not shown for clarity. The X-frame 12 is omitted in this example as therequired structural rigidity is provided to the display unit 1 inparticular by the combination of the housings 5, the side members 3, thescreen edge strips 17, and the screen backing slats 35.

For each housing 5, the aperture 6 is formed as a gap between thehousing 5 and the lid 33 when in place. The roll bar guide 9 comprisestwo upper short roll bars 41, 42 and a lower cogwheel roll bar 43 (shownonly in FIG. 10 for one housing 5 for clarity). The two upper short rollbars 41, 42 are mounted at both sides of the aperture 6 adjacent to itstop. The lower cogwheel roll bar 43 extends across the width of theaperture 6 adjacent to its bottom, and comprises of two cogwheels 44, 45mounted on a roll bar. Each roll-bar 41, 42, 43 is mounted in thehousing 5 such that it can rotate about its longitudinal axis. The rollbars 41, 42, 43 are arranged so that the screen 5 passes between theupper roll bars 41, 42 and the lower roll bar 43 when passing throughthe aperture 6.

The screen 5 has support slats 35 formed on its under side 32. The slats35 have a cross sectional shape in the form of a (partial) sector of acircle. This cross sectional shape allows the slats 35 to engage withthe recesses formed between the teeth of the two cogs 44, 45 of thelower cogwheel roll bar 43. As each slat 35 engages with the cogwheelroll bar 43 it is constrained in its alignment to be parallel to thecogwheel roll bar 43 and thereby perpendicular to the direction in whichthe screen 2 is being extended or retracted. This arrangement helpsmaintain the screen in a rectangular/square form.

Referring now to FIGS. 11 to 14, detail sections of the display device 1are shown, showing a part of one housing 5, side member 3, screen edgestrip 17, etc. Accordingly, in the following discussion in relation toFIGS. 11 to 14, a single instance of these features is generallydescribed. It should be noted, however, that the description appliesequally to all instances of the particular feature.

Referring now to FIG. 11 (which shows an enlarged detail of FIG. 10 fromabove), the channels 28 that store the side members 3 are positioned infront of the roller 4. This position, as opposed to positioning thechannels 28 behind the roller 4, has the advantage of reducing thetransition curvature 29 of the side-members 3 as they pass from theirextended open V-shape form through the aperture 24 to their closed form,which makes extension and retraction easier.

The screen edge strip 17 has two grooves 18, 19 formed in its undersiderunning along its length. The screen edge strip 17 comprises anunderside surface sheet 38 (which may conveniently be formed of ametal), which is attached to the underside of the screen edge strip 17,running along its length, and being positioned between the two grooves18, 19 such that its edges are approximately flush with the sides of thegrooves 18, 19. A series of tabs or projections 37 is formed in theunderside surface sheet 38 on each opposed edge and runs along itslength. The projections 37 overlap the underside grooves 18, 19. Theunderside surface sheet 38 may be biased in order to help retract andwind the screen 3 about the rollers 4.

Referring to FIG. 12, each side member 3 has an approximately V or Y or“wine glass” cross section shape when in its extended form. The end ofeach “leg” of the side member 3 has a series of apertures or recesses orperforations 39 running along its length which correspond to the seriesof projections 37 on the screen edge strip 17. When extended, the endsof the two legs of each side member 3 respectively fit into the twounderside grooves 18, 19 such that the projections 37 are received bythe perforations 39 in a reversible locking arrangement. When extended,the screen edge strip 17 and the two legs of the side member 3 form astructurally rigid member with a generally triangular cross sectionshape which provides structural rigidity and protection to the screen 3.When engaged with the screen edge strip 17, the two legs of the sidemember 3 may have a slight inward bias which helps maintain theengagement of the projections 37 with the perforations 39. Thearrangement of the perforations 39 and projections 37 has the advantageof providing a strong stable connection between the side member 3 andthe screen edge strip 17, and restricts any relative longitudinalmovement between them. The side member 3 locks to the screen edge strip17 from below only. This arrangement allows the top of the screen 3 tobe flat across its width with no structures extending above it. Thisarrangement also allows a side member 3 with a reduced cross sectionalarea, which in turn allows a smaller housing 5 to store it.

A guide member in the form of a prong 36 is mounted in the housings 5between each channel 28 and guide aperture 24. The prong 36 ispositioned such that, as the side member 3 retracts into the housing 5,the legs of the side member 3 are drawn past either side of the prong36. The free end of the prong 36 is sized and shaped so as to slightlyforce apart the legs of the side member 3 as they pass over the end ofthe prong 36 such that the perforations 39 in the ends of the legs ofthe side members 3 disengage with the projections 37 in the grooves 18,19 of the screen edge strip 17. The screen edge strip 17 passes abovethe prong 36 and is wound on the roller 4. Further inwards from its freeend, the prong 36 curves upwards such that, once disengaged from theside member 3, the screen edge strip 17 is lifted as it passes over theprong 36 such that the screen edge strip 17 is no longer positionedbetween the legs of the side member 3. The side member 3 is nowunobstructed by the screen edge strip 17 so that it can make thetransition to a substantially planar form so that it can be stored inthe channel 28.

The prong 36 performs similarly in reverse to engage the perforations 39and projections 37 when the screen 5 is being extended.

FIGS. 12, 13 and 14 most clearly show (in cross-section) the side memberpassing through the aperture 24. The side member 3 is preferablyarranged with a cross section shape like a wine glass. It is notpreferred to form the side member 3 from a bistable material in thisexample. It is preferred that the side member 3 is formed with a stableform that is intermediate between the open profile of its extended form(shown in FIGS. 12, 13, and 14) and a substantially planar profile. Whenthe side member 3 is extended, the grooves 18, 19 in the underside ofthe screen edge strip 17 hold the side member 3 in its extended form.When the side member 3 is retracted, the channel 28 holds the sidemember 3 in its substantially planar form.

The prong 36 may be provided with wheels or rollers, or a layer orcoating of a low friction material, such as PTFE, at its free end. Thisreduces the friction between the end of the prong 36 and the legs of theside member 3 and/or screen edge strip 17 as they slide over the prong36.

As can be seen most clearly in FIG. 14, the side member 3 has a flexibleedge 40 at its base to provide a smooth edge. The flexible screen edgestrip 17 has a shaped inward edge to support the screen backing slats 35forming the screen back 32.

Embodiments of the present invention have been described with particularreference to the examples illustrated. However, it will be appreciatedthat variations and modifications may be made to the examples describedwithin the scope of the present invention.

1. A display device, the display device comprising: an extendible screenthat is extendible in an extension direction from a relatively compactform to an extended form, the screen having a backing layer that hasincreased rigidity when planar to provide increased rigidity to thescreen when the screen is in its extended form, wherein the backinglayer is formed from a smart material.
 2. A display device according toclaim 1, wherein the smart material is capable of undergoing acurrent-assisted solid-state phase transition.
 3. A display deviceaccording to claim 1, wherein the smart material is a shape memoryalloy.
 4. A display device according to claim 3, wherein the smartmaterial is capable of undergoing a current-assisted solid-state phasetransition.
 5. A display device according to claim 1, wherein the screenis arranged to roll from the extended form to the relatively compactform.
 6. A display device according to claim 5, wherein the rollingscreen rolls about a single axis.
 7. A display device according to claim5, wherein the rolling screen rolls partly about a first axis and partlyabout a second parallel axis.
 8. A display device according to claim 1,comprising at least one housing which at least partially accommodatesthe screen when in said relatively compact form.
 9. A display devicecomprising: an extendible screen that is extendible in an extensiondirection from a relatively compact form to an extended form, the screenhaving a backing layer that has increased rigidity when planar toprovide increased rigidity to the screen when the screen is in itsextended form, wherein the backing layer comprises a plurality of slatswhich extend across the screen in a direction perpendicular to theextension direction and such that the screen can be rolled about atleast one axis parallel to the direction of the slats.
 10. A displaydevice according to claim 9, wherein the backing layer is formed from abistable material.
 11. A display device according to claim 9, whereinthe screen is arranged to roll from the extended form to the relativelycompact form.
 12. A display device according to claim 11, wherein therolling screen rolls about a single axis.
 13. A display device accordingto claim 11, wherein the rolling screen rolls partly about a first axisand partly about a second parallel axis.
 14. A display device accordingto claim 9, comprising at least one housing which at least partiallyaccommodates the screen when in said relatively compact form.